In general, contact lenses are produced in mass by a so-called cast-molding process, which involves thermo- or UV-induced free-radical polymerization of a lens-forming composition including vinylic monomers and/or vinylic macromers in molds. UV-induced polymerization process is generally preferred because its processing cycle is shorter than the thermo-induced polymerization process. In certain applications, it is desirable to incorporate UV absorbers into the ophthalmic lens. One approach is to copolymerize a polymerizable UV absorber with other lens-forming vinylic monomers and/or macromer so that the UV absorber is covalently attached to the copolymer. Copolymerizable benzotriazole, benzophenone and triazine UV absorbers, which include an ethylenically unsaturated group covalently linked to their UV-absorbing moieties, are known and have been used previously. However, there are several disadvantages associated with use of a known polymerizable UV-absorber. First, the efficiency of incorporation of the UV-absorber in lenses may not be certain. Second, a UV-absorber present in a lens forming composition can reduce the amount of UV radiation available to initiate polymerization and may even lower the efficiency of covalent incorporation of the UV absorber into resultant lenses. Unreacted UV absorbers generally must be removed from the lenses in one or more extraction processes. Third, a UV-absorber may result in ineffective or uneven photo-polymerization of the lens forming composition.
Therefore, there still exists a need for a cost-effective method for making UV-absorbing contact lenses.